1. Field of the Disclosure
This invention relates in general to music systems. More specifically, this invention provides an optical pickup to be used in connection with a pitch calculator system to create electrical signals in response to an input musical sound.
2. Description of the Prior Art
Electronic music synthesizers create varied musical sounds by generating various shaped wave forms at a desired pitch and amplitude. In general a synthesizer system will contain controls for varying the spectral content, harmonic content, amplitude, envelope shape, attach and delay time and other parameters that affect the timbre of musical sounds as perceived by the human ear. The operator of an electronic synthesizer thus has two major functions that must be performed. He must "shape" the wave, thus determining its timbre and character, and he must input the note or notes that the shaped wave form should assume.
There are two basic ways to input this note information. One is to use a standard piano keyboard as the input device. The problem with this method is that the output signal cannot be dynamically controlled in response to the input signal. Specifically, the volume of the output signal will not depend on the force with which the key is depressed, and must be separately controlled. This utilization of a piano-type keyboard also limits the synthesizer operation to those whose have the ability to play a keyboard instrument.
A more versatile method of providing "note" input is to use the musical signal from any musical instrument to control the synthesizer's sounds. Many advantages are obtained from this tecnhique. For one, a much larger class of people could operate an electronic synthesizer, as any musical instrument with which one is familiar could be used as the input source. Another advantage is that the output volume of the note from the synthesizer can be made to depend on the volume of the input note from the instrument.
Any musical instrument that is able to generate musical vibrations can be used as an input source to an electronic synthesizer, providing an appropriate interface is used. Different synthesizers accept different input signals such as: linear DC control voltages proportional to the pitch of the desired note, sine waves representing the pitch to be output, or digital data to a microprocessor controlled music synthesizer. Since a musical sound typically includes a number of harmonics or overtones of varying amplitude, a problem has existed in that a synthesizer could falsely detect more than one frequency present in a single note. In response to this, a number of devices called pitch detectors or frequency followers have been proposed. The operation of a typical pitch detector will be described herein.
There are four basic methods of entering the musical signal into the pitch detector. One is by playing the instrument in proximity to an electromagnetic microphone. Mechanical transducers, and electromagnetic pickups, and optical pickups attached to the instrument itself can also be used. This method is most often employed in conjunction with a stringed instrument.
Once an electrical signal corresponding to the musical sound has been entered into the pitch detector, a number of different methods can be used to extract the necessary information from the signal. This subject is discussed in my co-pending application, A Universal Pitch and Amplitude Calculator and Converter For a Musical Instrument, Ser. No. 768,447, and in U.S. Pat. Nos. 4,351,216 to Hamm, and 4,300,431 to deRocco, the disclosures of which are expressly incorporated herein by reference.
The present invention has as its objectives a new and improved optical pickup for use with an apparatus for calculating the pitch and amplitude of an input complex musical signal. New functions can be performed with this system, and many of the problems existing in the prior art are overcome by the novel methods of this invention.
When a pitch calculator as described in my co-pending application Ser. No. 768,447 or another similar pitch calculator is used with a stringed instrument, each string of the instrument must be connected to a separate pitch calculator circuit. Each pitch calculator circuit then detects the particular pith which has been emitted by the particular string. This pitch is then used as part of a control output for an electronic music synthesizer. As the circuitry in this and other similar pitch detector circuits typically detect a only single pitch (the fundamental frequency of the note), each string of the stringed instrument must have a separte pickup which is separately cabled to the pitch calculator system.
In a typical magnetic prior art pickup, as exemplfied by U.S. Pat. No. 4,137,811 to Kakehashi and U.S. Pat. No. 4,181,058 to Suenaga, a magnetic pickup was typically located below the plane comprising the plurality of strings of the instrument, and adjacent to other pickups which were detecting the note from the adjacent strings. As a result of this configuration, each magnetic pickup would detect predominantly the note from its associated string, but would also detect any notes emitted by adjacent strings. Since a typical pitch calculator cannot process polyphonically (that is, can only process one pitch at any given time), a standard magnetic pickup such as this could easily cause erroneous results.
Alternatives to the standard magnetic pickup are known in the prior art however. One such alternative is the use of a fiber optic entry system, such as described in U.S. Pat. No. 4,442,750 to Bowley. Bowley teaches running optical fibers in registery with the body of the musical instrument. The vibration of the body of the musical instrument then causes light modulation within these optical fibers which generates a fiber optic signal.
Optical pickups have also been taught in the prior art as exemplified by U.S. Pat. No. 4,297,938 to Kirby, and U.S. Pat. No. 3,733,953 to Ferber, disclosures of both of which are expressly incorporated herein by reference. Kirby teaches an optical detector of string motion for use as an electronic tuning aid for a stringed instrument. In Kirby, a light source is located above the plane of each string, and a light sensitive element such as a photoresistor is located below the plane of the string. An aperture is constructed around the photoresistor to admit a 3/16 inch round aperture of light which is claimed to be the optimal amount of light to detect the vibration of the string. When the string vibrates, the light impinging on the photoresistor is selectively obstructed so that the photoelectric current varies at the rate the string is vibrating at.
Conspicuously absent from any of the string pickup systems mentioned above is the ability to keep the electrical signal produced by a string from being interfered with by motion of adjacent strings. As discussed above, prevention of this interference is necessary for effective use with a pitch calculator system.
U.S. Pat. No. 3,733,953 to Ferber also teaches an optical electronic pickup system with light emitters above the plane of the instrument strings and light detectors below the stirngs. The movement of the string in the plane of the optical beam passing between the emitter and detector modulate the light beam according to the string vibration. In the Ferber system, each individual pickup is generally "C" shaped with the string passing through an open portion of the pickup. Each string is thereby surrounded by the frame of the pickup on top, bottom, and one side. The frame of an adjacent pickup obstructs the other side. In this way, each string is kept from interfering with the adjacent string by the structure of the pickup.
However, the Ferber design also suffers from many disadvantages. Firstly, due to the closed-in nature of the strings within the pickups, changing of strings would be a very difficult process, and may in fact require removal of parts of the pickup to locate the string in the proper place. To locate a string correctly within the Ferber pickup the string must be "threaded" through the pickup, as insertion of the string from above would presumably no longer be possible. Furthermore, the system in Ferber is an enclosed unit, as shown by part 22 of FIG. 1. As a minimum, some disassembly of this unit would be required, which could be a difficult and time consuming process. Since string changing is so often necessary in guitars, this could be a major disadvantage.
Another disadvantage of the prior art systems lie in the mechanics of stringed instrument playing. In a stringed instrument, the player depresses strings down to fret level in order to shorten the length of the string and thus make a higher pitch note. In certain stringed instruments, the string may also be stretched in order to vary the pitch of the note. This movement of the string by the player can tend to remove the vibration of the string out of the plane of the prior art infra-red pickups (and specifically those in Kirby and Ferber).
Also, Kirby and Ferber both teaches using optical detector with relatively wide admission apertures for impinging light. This has certain disadvantages which are discussed below.
The present invention overcomes the limitations and problems discussed above.